An alligator's tail length, T, varies directly as its body length, B means

T = kB, where k is constant

An alligator with a body length of 4.5 feet has a tail length of 4 feet:

4 = k*4.5

k*4.5 = 4

k = 4.5/4

thus the formula is:

T = (4.5/4)B

B = 5.4 ft for the tale we have

T = (4.5/4)*5.4

T = 6.075 ft

the tail length of an alligator whose body length is 5.4 feet is 6.075 ft.